Digital predistortion calibration

ABSTRACT

A method for digital predistortion (DPD) calibration in a wireless communication device is provided that includes transmitting, by transmission circuitry of the wireless communication device, a plurality of pulses, where each pulse corresponds to an amplitude step in a pattern of amplitude steps, where the amplitude steps are separated by silence gaps, receiving each pulse in receiver circuitry of the wireless communication device, generating, by an accumulator component of the wireless communication device, an accumulated sample for each pulse based on a plurality of samples output by the receiver circuitry for the pulse, and computing, by a processor of the wireless communication device, amplitude dependent gain (AM/AM) and amplitude dependent phase shift (AM/PM) values for each accumulated sample.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/148,304 filed Jan. 13, 2021, which is a continuation of U.S. patentapplication Ser. No. 16/288,094 filed Feb. 27, 2019, now U.S. Pat. No.10,924,068, both of which are incorporated herein by reference in itsentirety.

BACKGROUND

Wireless sensor networks are typically implemented using low powersingle chip devices operating on AA batteries, e.g., wirelesscommunication devices. Such devices include a Wi-Fi radio with anintegrated radio frequency (RF) power amplifier (PA). The RF PA is anactive component creating high power levels and needs to operate withhigh efficiency to help conserve power. However, highly efficientoperation of a PA when using amplitude modulated signals typicallyresults in nonlinear distortions that degrade the performance of thenetwork. For this reason, regulatory requirements limit the amount ofdistortion that is tolerable, commonly in the form of limits on thepower emitted in neighboring frequency channels. In view of theserequirements, improving PA linearity and reducing distortions isimportant.

One technique that can be used to improve PA linearity is digitalpredistortion (DPD) of the PA based on calibration parameters. The DPDmay be performed when the device is powered on and may be performed atother times as well. Current techniques for DPD calibration may be tootime consuming and/or consume too much power to be used in batteryoperated devices.

SUMMARY

Embodiments of the present disclosure relate to methods and apparatusfor digital predistortion (DPD) calibration. In one aspect, a method forDPD calibration in a wireless communication device is provided thatincludes transmitting, by transmission circuitry of the wirelesscommunication device, a plurality of pulses, where each pulsecorresponds to an amplitude step in a pattern of amplitude steps, wherethe amplitude steps are separated by silence gaps, receiving each pulsein receiver circuitry of the wireless communication device, generating,by an accumulator component of the wireless communication device, anaccumulated sample for each pulse based on a plurality of samples outputby the receiver circuitry for the pulse, and computing by a processor ofthe wireless communication device, amplitude dependent gain (AM/AM) andamplitude dependent phase shift (AM/PM) values for each accumulatedsample.

In one aspect, a wireless communication device is provided that includestransmission circuitry, receiver circuitry coupled to the transmissioncircuitry by a feedback loop to receive pulses transmitted by thetransmission circuitry, an accumulator component coupled the receivercircuitry to receive samples output by the receiver circuitry, aprocessor coupled to the transmission circuitry and to the accumulatorcomponent, and a non-transitory computer readable storage medium storinga program for digital predistortion (DPD) calibration for execution bythe processor, the program including instructions to transmit, by thetransmission circuitry, a plurality of pulses, where each pulsecorresponds to an amplitude step in a pattern of amplitude steps, wherethe amplitude steps are separated by silence gaps, receive each pulse inthe receiver circuitry via the feedback loop, generate, by theaccumulator component, an accumulated sample for each pulse based on aplurality of samples output by the receiver circuitry for the pulse, andcompute amplitude dependent gain (AM/AM) and amplitude dependent phaseshift (AM/PM) values for each accumulated sample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example 5 GHz band wireless local areanetwork (WLAN) radio including circuitry for digital predistortion (DPD)and DPD calibration that can be used in a battery operated wirelesscommunication device;

FIG. 2 is a graph illustrating an amplitude ramp for DPD calibration;

FIG. 3 is graph of an example pattern of interlaced high and lowamplitude steps with silence gaps for DPD calibration;

FIG. 4 is a graph of an example pattern of seven interlaced high and lowamplitude steps with silence gaps between amplitude steps for DPDcalibration;

FIG. 5 is a block diagram of an example WLAN radio showing additionaldetail of the distortion estimation component of the WLAN radio of FIG.1 ;

FIG. 6 is a flow diagram of a method for DPD calibration;

FIG. 7 is a block diagram of an example wireless communication device;and

FIG. 8 is a block diagram of an example wireless sensor device.

DETAILED DESCRIPTION

Specific embodiments of the disclosure will now be described in detailwith reference to the accompanying figures. Like elements in the variousfigures are denoted by like reference numerals for consistency.

Embodiments of the disclosure provide for calibration of a digitalpredistortion (DPD) component in a Wi-Fi radio. The nonlinearcharacteristics of a radio frequency (RF) power amplifier (PA) arecharacterized by the amplitude dependent gain (amplitude modulation(AM)/AM or AM2AM) and amplitude dependent phase shift (AM/phasemodulation (PM) or AM2PM) of the PA. The essence of digitalpredistortion is that the amplitude and phase of input signals arepreprocessed to compensate for the AM/AM and AM/PM distortion caused bythe PA.

FIG. 1 is a block diagram of an example 5 GHz band wireless local areanetwork (WLAN) radio 100 including circuitry for digital predistortion(DPD) and DPD calibration that can be used in a battery operatedwireless communication device. The example radio 100 includestransmission circuitry 102 that includes transmission (TX) analogcircuitry 103 and a power amplifier (PA) 106 coupled to the TX analogcircuitry 103. The TX analog circuitry 103 includes circuitry to preparesignals to be transmitted for amplification by the PA 106. The exampleradio 100 also include auxiliary receiver circuitry 104 coupled to thetransmission circuitry 102 by a feedback loop 112 for use in determiningDPD calibration parameters for the PA 106. The inputs to the radio 100are the in-band (I) and quadrature (Q) components of an RF signal to betransmitted.

For efficiency in terms of power consumed and power delivered, the PA106 should be operated near its saturation point (PSAT). However,operating a PA near PSAT introduces nonlinear distortions at the outputof the PA and degrades the bit error rate (BER) performance. Tocompensate for AM/AM and AM/PM distortion caused by the PA 106 whenoperated near PSAT, the I and Q signals are pre-distorted by the DPDcomponent 108. The DPD component 108 includes a complex gain adjusterthat controls the amplitude and phase of the input signal. The amount ofpredistortion is controlled by entries in a calibration lookup tablethat interpolate the AM/AM and AM/PM nonlinearities of the PA 106. Putanother way, the amount of predistortion is controlled by correctionvalues for the AM/AM and AM/PM nonlinearities of the PA 106 stored inthe calibration lookup table. The level of the envelope of the inputsignal is used to index the calibration lookup table. The complex gainadjuster, given correction values from entries in the calibration lookuptable, provides inverse nonlinear characteristics to that of the PA 106.

The correction values of the entries in the lookup table are determinedby a calibration process performed using the auxiliary receivercircuitry 104 to characterize the PA 106. The calibration is performedwhen the radio 100 is powered on. The calibration may also be performedduring operation of the radio 100, e.g., periodically to accommodatechanges in characteristics of the PA 106 due to factors such astemperature change, voltage variations, channel changes, and aging.

In one approach to calibration, a continuous wave (CW) tone withcontinuous ramping amplitude is transmitted by the transmissioncircuitry 102 and fed back from the output of the PA 106 to the input ofthe auxiliary receiver circuitry 104 via the feedback loop 112. Thenumber of amplitude steps in the continuous ramp can be determined basedon the characteristics of the PA 106. The graph of FIG. 2 illustrates anexample of such an amplitude ramp. The distortion estimation component110 receives the digital signals output by the auxiliary receivercircuitry 104 at each step and estimates the AM/AM and AM/PM valuesrepresenting the distortion introduced by the PA at the correspondingamplitude. The estimated AM/AM and AM/PM values for the amplitude stepsare then used to determine the correction entries of the calibrationlookup table used by the DPD component 108.

Values for AM/AM and AM/PM are estimated for each step in the continuousramp as follows. At each amplitude step, several samples of a complex CWtone are transmitted at that amplitude and received in the auxiliaryreceiver circuitry 104. An accumulated sample for the amplitude isgenerated based on the samples output by the auxiliary receivercircuitry 104. In general, the output samples are down converted tobaseband and, after a specified number of samples has been output by theauxiliary receiver circuitry 104 and down converted, a filter is appliedto the down converted samples to generate the accumulated sample. Themagnitude and angle of the accumulated sample indicate AM/AM and AM/PM,respectively, for the step.

For example, to down convert an output sample to baseband, the outputsample can be delay matched with the corresponding sample input to thetransmission circuitry 102 and then multiplied with the complexconjugate of the corresponding input sample. And, to generate theaccumulated sample, an averaging filter can be applied to the downconverted samples.

Using a CW tone with a continuous ramp involves continuously increasingcurrent which can cause a power management failure when the batteries ofthe wireless communication device cannot supply the needed current. Forexample, under high current demand, the battery voltage can dip belowthe safety margin of voltage sensors in the device, causing the deviceto shut down. In some embodiments, rather than transmitting a continuousCW tone with multiple increasing amplitude steps, a pattern of amplitudesteps separated by silence gaps is transmitted. This pattern may bereferred to as a transmission pattern herein. Breaking the rampingcontinuous tone with silence gaps avoids the continuous current surgefrom the battery and allows the bypass capacitor of the battery torecharge and supply current for the next amplitude step while avoiding adip in the battery voltage.

When DPD calibration is performed, network traffic may be interruptedfor the duration of the calibration. Adding silence gaps betweenamplitude steps can unacceptably increase the amount of time needed forcalibration, requiring a tradeoff between the number of amplitude steps,the pulse width, also referred to as the number of samples in the pulse,of each step, and the silence gap lengths between amplitude steps. Forexample, assuming sixty-four amplitude steps, a pulse width ofapproximately 2 us, and a silence gap length of approximately 10 us, thecalibration time would be greater than 750 us.

The pulse widths and amplitudes of the amplitude steps, the pattern oramplitude ordering of the amplitude steps, the number of samples perpulse, and the silence gap lengths can be determined empirically. Todetermine the transmission pattern of the amplitude steps, the pulsewidth and amplitude of each amplitude step, the samples per pulse, andthe silence gap lengths, three metrics can be considered: transmissionperformance, calibration time, and power consumption. On the performanceside, two metrics are considered: error vector magnitude (EVM) andspectral mask. The goal is to find optimal pulse widths and silence gaplengths, and a transmission pattern that reduce battery currentconsumption while minimizing calibration time and not violating EVM andspectral mask metrics.

In some embodiments, the transmission pattern of the amplitude steps andsilence gaps is one in which each amplitude step increases in amplitudefrom the previous amplitude step. While this pattern may increasecurrent demand for the continuously increasing amplitudes of pulses, thecurrent demand may not be an issue provided the silence gap lengthsbetween the amplitude steps are sufficiently long to allow the bypasscapacitor of the battery to recharge. However, using sufficiently longsilence gap lengths can unacceptably increase the time needed forcalibration. In some embodiments, the transmission pattern is one inwhich high and low amplitude steps are interlaced, i.e., alternated,with silence gaps between the amplitude steps. The interlacing reducesthe silence gap length needed for recovery, thus reducing thecalibration time for the same number of amplitude steps. FIG. 3 is agraph of an example of one pattern of interlaced high and low amplitudesteps with silence gaps between amplitude steps.

In some embodiments, the number of amplitude steps in the transmissionpattern is equal to the number of entries in the calibration lookuptable. However, the slow varying nature of AM/AM curves can be exploitedto further reduce the number of transmitted amplitude steps forcalibration, thus reducing the calibration time. In some embodiments, inorder to reduce the time needed for calibration, the number of amplitudesteps transmitted is less than the number of calibration lookup tableentries, e.g., seven amplitude steps as compared to thirty-two tableentries, and other AM/AM and AM/PM values needed to determine thecorrection values for the calibration lookup table entries areinterpolated from the AM/AM and AM/PM values computed for theaccumulated samples of the smaller number of amplitude steps.

For example, if the calibration lookup table has thirty-two entries andthe transmission pattern is seven amplitude steps at selected amplitudesrepresented in the lookup table, the AM/AM and AM/PM values used todetermine the other twenty-five table entries are interpolated from theAM/AM and AM/PM values computed for the seven accumulated samples of theseven amplitude steps. In such embodiments, the number and amplitudes ofthe amplitude steps can be determined empirically along with the pulsewidths, silence gap lengths, and transmission pattern. FIG. 4 is a graphof an example of a transmission pattern of seven interlaced high and lowamplitude steps with silence gaps between amplitude steps.

FIG. 5 is a block diagram of an example WLAN radio 500 showingadditional detail of the distortion estimation component 110 of FIG. 1 .The distortion estimation component 110 includes a calibration tonegenerator 513, a processor 510, and an accumulator component 514. TheDPD calibration process is controlled by calibration software executingon the processor 510. The processor 510 includes one or more suitableprocessors such as programmable general-purpose or special-purposemicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), programmable controllers, programmablelogic devices (PLDs), or the like, or a combination of such devices. Thesoftware instructions to perform the calibration process in the radio100 to generate the entries in the calibration lookup table of the DPDcomponent 108 are stored in a non-transitory computer readable storagemedium (not shown) such as random access memory (RAM), read-only memory(ROM), and flash memory.

The multiplexer 509 selects between the input I and Q signals and thesignals from the calibration tone generator 513 based on a controlsignal set by the processor 510. The calibration tone generator 513includes programmable circuitry to generate tones (pulses) ofconfigurable duration and amplitude.

The accumulator component 514 includes programmable circuitry to downconvert and accumulate a specified number of samples of a transmittedpulse output from the auxiliary receiver circuitry 104. The accumulatorcomponent 514 further includes circuitry to filter the down convertedsamples to generate an accumulated sample for a transmitted pulse andprovide the accumulated sample to the processor 510.

In some embodiments, additional reduction in current consumption isachieved by disabling one quadrature channel of the auxiliary receivercircuitry 104 during DPD calibration. Either quadrature channel can bedisabled which can result in a reduction in current consumption ofapproximately 50% when processing received signals. When only onequadrature channel is used, the level of the image tone and the originaltone are equal. The accumulator component 514 is designed to cancel thefrequencies of the image tone because if the level of the image tone ishigh, the quality of the original signal can be negatively impacted.

In such embodiments, the transmitted tone frequency and the number ofsamples accumulated per amplitude step are chosen such that nulls in thefrequency response of the filter used by the accumulator component 514are multiples of the tone frequency, thus cancelling the image tone.Further, the frequency of the digital clock affects the choice of tonefrequency and the number of samples to be accumulated. For example,assume the clock frequency is 80 MHz and the number of samples is 64.The lowest possible frequency that can be resolved given theseassumptions is 80e6/64=1.25 MHz. Finer frequency resolutions can beachieved by accumulating more samples.

FIG. 6 is a flow diagram of a method for DPD calibration that can beperformed by the WLAN radio 100 of FIG. 1 and the WLAN radio 500 FIG. 5. The method assumes a predetermined transmission pattern of amplitudesteps in which the pulse width, amplitude, silence gap length, andnumber of samples to accumulate is specified for each step. In someembodiments, the widths of the pulses are identical, the silence gaplengths are identical, and the number of samples to accumulate areidentical for each step of the transmission pattern. In someembodiments, the pulse width, silence gap length, and/or number ofsamples to accumulate can differ from step to step in the transmissionpattern. In some embodiments, the transmission pattern is one in whichhigh and low amplitude steps are interlaced, i.e., alternated. In someembodiments, one channel of the auxiliary receiver circuitry 104 isdisabled.

For each pulse in the transmission pattern, the calibration softwareexecuting on the processor 510 configures 600 the calibration tonegenerator 513 to generate a pulse of the specified width and amplitude,and also configures 602 the accumulator component 514 to accumulate thespecified number of samples of the pulse. The samples of the pulse aretransmitted 604 through the transmission circuitry 102 and received 605in the auxiliary receiver circuitry 104 via the feedback loop 112.

The accumulator component 514 receives the samples output by theauxiliary receiver circuitry 104 and generates 606 an accumulated samplefrom the specified number of samples. Generation of an accumulatedsample includes down converting each output sample to baseband, and,after the specified number of samples has been received, filtering thesamples to determine the accumulated sample. In some embodiments, anaveraging filter is used to determine the accumulated sample. Theaccumulated sample is then provided to the processor 510.

If the pulse is not the last pulse 608 of the transmission pattern, thecalibration software waits 610 until the specified silence gap lengthhas elapsed, and then repeats steps 600-606 for the next pulse in thetransmission pattern. Once the last pulse 608 has been transmitted, thecalibration software computes 612 the AM/AM and AM/PM values for each ofthe accumulated samples, and computes 614 the correction values for thecalibration lookup table entries based on the AM/AM and AM/PM values ofthe accumulated samples. The correction values are stored incorresponding calibration lookup table locations and used by the DPDcomponent 108 during normal operation of the WLAN radio 100. In someembodiments, the transmission pattern includes fewer transmittedamplitude steps than are needed to determine the calibration lookuptable entries. In such embodiments, the additional AM/AM and AM/PMvalues are interpolated from the AM/AM and AM/PM values computed for theaccumulated samples resulting from the transmission pattern.

FIG. 7 is a simplified block diagram of an example wirelesscommunication device 700. The wireless communication device 700 includesan antenna 701, a transceiver component 702, a processor component 704,a memory component 706, and an application component 708. The antenna701 is configured to receive and transmit radio frequency (RF) signals.The transceiver component 702 is configured to modulate received RFsignals and to modulate RF signals to be transmitted. The transceivercomponent 702 is further configured to perform DPD and DPD calibrationas described herein. For example, the transceiver component 702 caninclude circuitry for DPD and DPD calibration such as that of FIG. 1 andFIG. 5 . The memory component 706 may include any suitable memory suchas random access memory (RAM), read-only memory (ROM), flash memory, orthe like, or a combination of such memory. The memory component 706 maybe a non-transitory computer readable storage medium storing a programfor execution by the processor component 704. The application component708 is configured to perform the function of the wireless communicationdevice 700, e.g., controlling an alarm, controlling a light, temperaturesensing, etc.

The processor component 704 includes one or more suitable processorssuch as programmable general-purpose or special-purpose microprocessors,digital signal processors (DSPs), application specific integratedcircuits (ASICs), programmable controllers, programmable logic devices(PLDs), or the like, or a combination of such devices.

FIG. 8 is a simplified block diagram of an example system-on-chip (SOC)800, e.g., a wireless communication device, configurable to perform DPDcalibration as described herein. The example SOC 800 depicted is aCC3220x SimpleLink™ Wi-Fi® Wireless Microcontroller Unit (MCU)System-on-Chip (SOC) available from Texas Instruments which can includesupport for DPD calibration as described herein. A brief description ofthe CC3220 is provided herein. A detailed description of the CC3220x isprovided in Texas Instruments publication SWAS035A, “CC3220 SimpleLink™Wi-Fi® Wireless and Internet-of-Things Solution, a Single-Chip WirelessMCU,” September 2016, revised February 2017, which is incorporated byreference herein in its entirety.

The SOC 800 provides two execution environments, a user applicationenvironment implemented by the application MCU subsystem 802 and anetwork environment to execute Wi-Fi and Internet logical layersimplemented by the network processor subsystem 804. The applications MCUsubsystem 802 incorporates an ARM® Cortex®-M4 MCU as the main processorwith embedded random access memory (RAM) and optional integrated flashmemory. The network processor subsystem 804 incorporates a WI-FIInternet-on-a-chip™ dedicated ARM MCU and Wi-Fi transceiver circuitry.In some embodiments, the Wi-Fi transceiver circuitry includes circuitryfor DPD and DPD calibration such as that of FIG. 1 and FIG. 5 .

The SOC 800 also incorporates RAM 814 that can be used for both storageof application data and execution of application code, and a ROM 816.The SOC 800 further incorporates peripheral interfaces 806 such as acamera interface and interfaces for serial peripheral interface (SPI),inter-integrated circuit (I²C), secure digital (SD) memory, inter-ICsound (I2S), and universal asynchronous receiver-transmitter (UART)protocols. Analog interfaces 808 in the SOC 800 includeanalog-to-digital converters (ADC) and pulse width modulation (PWM). TheSOC 800 also includes a power management subsystem 812 and systemsupport circuitry 810 such as oscillators, general purpose input/output(GPIO) pins, timers, and internal direct memory access (DMA).

Software instructions implementing DPD calibration as described hereincan be stored in a computer readable medium on the SOC 800 such as therandom access memory (RAM) 814, or the read-only memory (ROM) 816, orthe ROM in the network processor subsystem 804 and executed by aprocessor in the network processor subsystem 804.

Other Embodiments

While the disclosure has been described with respect to a limited numberof embodiments, those having benefit of this disclosure will appreciatethat other embodiments can be devised which do not depart from the scopeof the disclosure as disclosed herein.

Embodiments are described herein in which some functionality of the DPDcalibration is performed by a processor executing software instructions.In other embodiments, some or all of this functionality can be performedin a hardware accelerator.

Embodiments are described herein in which an averaging filter is appliedto generate the accumulated sample. Other suitable filters can also beused.

In some embodiments, the silence gap lengths between the pulses havediffering lengths to avoid transmission of periodic pulses that can bedetected as radar signals. For example, each differing gap length can bechosen randomly or can be set in the transmission pattern.

Embodiments are described herein referring to a single calibrationlookup table. In some embodiments, there are separate calibration tablesfor AM/AM correction values and AM/PM correction values. In someembodiments, there are multiple AM/AM and AM/PM calibration lookuptables corresponding to different gain settings of the transmissioncircuitry.

Embodiments are described herein in which each step of a transmissionpattern has a different amplitude. In other embodiments, some amplitudesteps may have the identical amplitude. For example, smaller pulsewidths can be used for high amplitude steps because such amplitude stepshave high SNR. However, lower amplitude steps have lower SNR and thepulse widths need to be larger to achieve more accurate filteringresults. To reduce current consumption for lower amplitudes that needlarger pulse widths, multiple amplitude steps of a smaller pulse widthwith the identical amplitude can be transmitted with silence gapsbetween rather than transmitting the single large pulse.

It is therefore contemplated that the appended claims will cover anysuch modifications of the embodiments as fall within the true scope ofthe disclosure.

What is claimed is:
 1. A method comprising: receiving, by a receiver, acalibration signal, wherein the calibration signal includes a pattern ofalternating amplitude steps separated by a silence gap length, whereinthe amplitude steps include a first set of amplitude steps that increasein amplitude over time interleaved with a second set of amplitude stepsthat decrease in amplitude over time; determining, by the receiver, aplurality of sample signals for each of the amplitude steps; generating,by the receiver, an accumulated sample signal for each of the amplitudesteps based on the plurality of sample signals; determining, by thereceiver, a first value and a second value for the accumulated samplesignal for each of the amplitude steps; and determine, by the receiver,a correction value based on the first value and the second value for theaccumulated sample signal for each of the amplitude steps.
 2. The methodof claim 1, wherein: the first value is an amplitude dependent gain(AM/AM) value; and the second value is an amplitude dependent phaseshift (AM/PM) value.
 3. The method of claim 1, further comprising:receiving an input signal that includes an in-band (I) component and aquadrature (Q) component.
 4. The method of claim 1, wherein: thedetermining of the first value and the second value occurs after a lastpulse is received.
 5. The method of claim 1, further comprising: inresponse to a number of the amplitude steps below a threshold:generating, by the receiver, a set of interpolated first values and aset of interpolated second values, wherein the set of interpolated firstvalues is based on the first value for the accumulated sample signal foreach of the amplitude steps and the set of interpolated second values isbased on the second value for the accumulated sample signal for each ofthe amplitude steps.
 6. The method of claim 5, wherein: the correctionvalue is further based on the set of interpolated first values and theset of interpolated second values.
 7. The method of claim 1, wherein apulse width of each of the amplitude steps is identical.
 8. The methodof claim 1, wherein a number of amplitude steps of the pattern ofalternating amplitude steps depends on the silence gap length and apulse width of each amplitude step.
 9. A device comprising: a receiverconfigured to sample a signal having a pattern of alternating amplitudesteps separated by a silence gap length, wherein the receiver isconfigured to provide a sample signal, wherein the pattern ofalternating amplitude steps includes a first set of steps that increasein amplitude over time interleaved with a second set of steps thatdecrease in amplitude over time; an accumulator coupled to the receiverand configured to receive the sample signal and determine an accumulatedsample signal for each of the amplitude steps; and a processor coupledto the accumulator, wherein the processor is configured to executeinstructions stored on a non-transitory computer readable storage mediumthat when executed cause the processor to: determine a first value and asecond value for the accumulated sample signal for each of the amplitudesteps; and determine a correction value based on the first value and thesecond value for the accumulated sample signal for each of the amplitudesteps.
 10. The device of claim 9, wherein: the first value is anamplitude dependent gain (AM/AM) value; and the second value is anamplitude dependent phase shift (AM/PM) value.
 11. The device of claim9, wherein: the signal includes an in-band (I) component and aquadrature (Q) component.
 12. The device of claim 9, wherein: theprocessor is configured to determine the first value and the secondvalue after a last pulse is received.
 13. The device of claim 9, furthercomprising: in response to a number of the amplitude steps below athreshold: the processor is configured to determine a set ofinterpolated first values and a set of interpolated second values,wherein the set of interpolated first values is based on the first valuefor the accumulated sample signal for each of the amplitude steps andthe set of interpolated second values is based on the second value forthe accumulated sample signal for each of the amplitude steps.
 14. Thedevice of claim 13, wherein: the correction value is further based onthe set of interpolated first values and the set of interpolated secondvalues.
 15. The device of claim 9, wherein a pulse width of each of theamplitude steps is identical.
 16. The device of claim 9, wherein anumber of amplitude steps of the pattern of alternating amplitude stepsdepends on the silence gap length and a pulse width of each amplitudestep.